This invention relates to an adaptive diversity receiver for digital communications and, more particularly, to a receiver capable of automatically estimating the characteristics of transmission channels and adaptively providing optimum receiver characteristics.
Diversity receivers have been used extensively in reducing fading in communication. However, in the presence of frequency selective fading, deep notches are formed in the transmission frequency band resulting in deteriorated transmission performance and transmission errors.
One solution to this problem is proposed in U.S. Pat. No. 3,879,664 to Monsen which discloses an adaptive diversity receiver using a decision feedback automatic equalizing technique, as illustrated in FIG. 1. Such a conventional receiver is generally satisfactory in steady state. However, since the receiver is designed to control tap gains of a plurality of adaptive forward transversal filter equalizes 13 to minimize an error signal produced from the combined output of these equalizers, it consequently requires a very long period of time for each tap gain to assume an optimum value. This may be shown by the fact that the eigenvalues of a coefficient matrix in a simultaneous linear equation are diversified for determining optimum tap gains. A detection error produced in a data detector and error generator 16 is fed through modulator 20 to the equalizers 13 which offset such an error signal before the tap gains of these equalizers may be updated. The equalizers thus fail to provide optimum adaptive equalization.